I can see some to the porous spots that will leak. I am not sure how to go about fixing these spots.
With the water jacket all cleaned up - you might consider taping off all the holes and then sloshing gas tank sealer around in there:
POR15 tank sealer While this will surely make it water tight - it might act as insulator and impact heat transfer from the head to the coolant.
I used this in my gas tank - it cures hard as rock.
